It seems just as inhospitable, but seemingly the entire area under the water has no soft kill, and there are a few spots where you can poke your head out of the water with no soft kill too. The area is kind of a mess, with some geometry lacking collision and some holes where you can fall through the map, plus if you go too far out from the shoreline you'll hit a hard kill, and visibility is really low and a little uneven, but it looks like a reasonable underwater environment. The bright side (aside from it just letting you get out there and spawn things) is that the total forgeable area is relatively large and you can go back to shore easily-- the invisible walls only stop you from going out, not in, and the soft kill zone can be crossed before it kills you.
In short, it's limited, but we finally get to forge underwater again! This is definitely in the top 3 things I'm most excited about from this update.